The present invention relates to a hearing apparatus, particularly a hearing aid, having a microphone for picking up ambient sound from the vicinity of a user. The present invention also relates to a corresponding method for operation of a hearing aid.
In conventional hearing aids, it is impossible to distinguish between the hearing aid wearer's own voice and an external sound source. This can lead to artifacts and incorrect response in various hearing aid algorithms, for example:                a) In the case of the automatic gain control (AGC), the gain is automatically reduced for high sound levels. If the sound level were to change suddenly, repeatedly and successively, then the gain would also be varied to a correspondingly major extent. This means that, for example, ambient noise or microphone noise is amplified differently depending on the useful sound level, and this is perceived as a pumping effect by the hearing aid wearer. In order to avoid these pumping effects, the AGC transient times, i.e., the time or time constant for readjustment of the gain, is typically chosen to be relatively long. However, this means that the user's relatively loud own voice (measured at the hearing aid) during a conversation with a relatively quiet conversation partner results in the AGC producing excessively low gain levels in transitional phases. Specifically, if the conversation partner speaks immediately after the hearing aid wearer has stopped speaking, the AGC is in the transient phase, and the gain is correspondingly low. This means that the gain is not increased sufficiently quickly for the generally quieter speech signals of the conversation partner, so that the first syllables or words may possibly not be understood, owing to lack of gain.        b) The approach of an “intelligent directional microphone”, which is activated only when a speech source is detected from the 0° forward direction, fails since the user's own voice is detected as a 0° source, and the directional microphone is disadvantageously also activated for a conversation partner at the side.        c) Blind source separation (BSS) algorithms attempt to use statistical methods to separate the superimpositions of the useful sound and the various interference signals that are present in the microphone signals. In this case as well, the user's own voice is identified as a separate source, which interferes with the extraction of the actual useful signal, which is generally likewise a speech signal.        
The European patent document number EP 1 251 714 A1 discloses a digital hearing aid system in which an occlusion subsystem compensates for the gain of the hearing aid user's own speech in the auditory channel. In this case, an undesirable signal which is received from a rearward microphone is fed back, and is subtracted from the useful signal.
U.S. Pat. No. 6,041,129 also discloses a hearing aid in which the hearing aid user's own voice is amplified or attenuated. In this case, the sound which is transmitted by bone conduction is detected via an accelerometer or a motion sensor.
The German patent document number DE 33 25 031 C2 describes an infrared headset with two microphones. Their signals are supplied in antiphase to an amplifier, thus preventing or suppressing the transmission of the user's own voice.
Furthermore, the German patent specification number DE 103 32 119 B3 discloses a hearing aid which can be worn in the ear and has a second microphone and a second earpiece, which are arranged in a ventilation channel. The signal for the second earpiece is phase-shifted in order to avoid sound being supplied directly to the hearing.